On Fri, 2005-12-30 at 16:27 +0530, Parag N(पराग़) wrote: > Hi, > On 12/30/05, Arjan van de Ven <arjan@xxxxxxxxxxxxx> wrote: > > On Fri, 2005-12-30 at 15:39 +0530, Parag N(पराग़) wrote: > > > Hi, > > > > > > On 12/30/05, Tetsuo Handa <from-kernelnewbies@xxxxxxxxxxxxxxxxxxx> wrote: > > > > Hi, > > > > > > > > kishore wrote: > > > > > I am using kmalloc in my module. It returned NULL; by that i understood > > > > > there may be some scarcity in allocating the requested amount of memory ( i > > > > > requested for 64 bytes). I returned -ENOMEM, but i thought there may be some > > > > > way to return error number rather than what am using. > > > > The kmalloc() can allocate up to 128 Kilo Bytes. > > > > Allocation for only 64 Bytes SHOULD NOT FAIL! > > > > I doubt you passed wrong parameters to kmalloc(). > > > > > > > I think you have to use kmalloc(64,GFP_ATOMIC) then u will not > > > get any memory allocation error. > > > > GFP_ATOMIC allocations are MORE likely to fail actually! > > (and are also more likely to bring the VM into big trouble so should be > > avoided if at all possible) > > > > > What leads me to think to use GFP_ATOMIC is following explanation for flags > GFP_ATOMIC The allocation is high-priority and does not sleep. This > is the flag to use in interrupt handlers, bottom halves and other > situations where you cannot sleep. > GFP_KERNEL This is a normal allocation and might block. This is the > flag to use in process context code when it is safe to sleep. > If kmalloc fails for allocating memory thru' GFP_KERNEL which > might be case of blocking request of kmalloc then i thought to use > high priority allocation flag. > If i am wrong correct me. the thing is.. with GFP_KERNEL the kernel is allowed to do IO (eg swap or write back dirty pagecache) so it can actually free memory a lot better to give you some, than with GFP_ATOMIC. Eg with GFP_ATOMIC you tie the hands of the VM, so it can do less work to make the allocation succeed. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
